Conventionally, a coupling structure in which multiple members are integrated by a stud bolt is known. Described in Patent Document 1 (JP 4702806 B2) is a structure including a flange and a cylinder head which are provided in an exhaust manifold and integrated by the stud bolt. The stud bolt extends through a through-hole made on the flange and is screwed to a female thread made on the cylinder head. A double nut is screwed to the stud bolt on a side of the flange that is opposite from the cylinder head. The double nut fixes the flange and the cylinder head. The stud bolt has a hexalobular external on an end opposite from the cylinder head. The hexalobular external is fitted in protrusions that are made on an inner wall of a through-hole of a lock plate. The fixing plate is fixed by a hex bolt to the cylinder head and prevents the double nut screwed to the stud bolt from loosing.
In the coupling structure described in Patent Document 1, the double nut engaged with the stud bolt is exposed outside of the flange and the cylinder head. Moreover, the lock plate is easily removed from the hexalobular external of the stud bolt by removal of the hex bolt. Therefore, if a tool such as a spanner is engaged with the double nut and then the stud bolt is rotated with the double nut about an axial direction, a linkage of the exhaust manifold and the cylinder head may be separated. If the multiple members integrated by the stud bolt are dismantled with evil intent, the members may be stolen.